Recently, portable devices represented by cellular phones have been thriving. Design of a portable device as well as higher functionality and higher performance of the portable device has been regarded as important. Then, in order to improve usability and appearance, a curved surface is being in heavy usage for the shape of a case of the portable device.
In a conventional mount board mounted within the case of the portable device, however, electronic components such as a semiconductor package are mounted on a flat board. Thus, it is difficult to efficiently arrange the electronic components within the case formed of various curved surfaces. For this reason, when the design is given priority, there is a problem that the size of the device may increase. Accordingly, it frequently happens that a design compromise must be inevitably made. Thus, it is strongly desired to put into practical use a board having a curved surface in conformity with the curved surface of the case, which is excellent in component arrangement efficiency within the case.
On the other hand, as a semiconductor package suited to the portable device, for which size reduction is required, a semiconductor package (a semiconductor device) as shown in FIG. 17 may be pointed out. In this semiconductor package, solder balls are arranged on a bottom surface of the package in a lattice form as connecting terminals. Such a package is described in Patent Document 1 and is referred to as a BGA (Ball Grid Array), a CSP (Chip Size Package), or a WL-CSP (Wafer Level Chip Size Package). Such a package is extensively used because more terminals can be arranged on this package with a smaller occupied area.
As a method of mounting this semiconductor package on the board, there is adopted the method of printing a cream solder on pads of the board using a metal mask, and melting the solder by reflowing after the semiconductor package has been mounted, thereby obtaining mechanical and electrical connection.
[Patent Document 1]    JP Patent No. P3395164 (FIG. 1)
[Patent Document 2]    JP Patent Kokai Publication No. JP-P2003-318218A (FIG. 2)